Conway's game of life in ansi c

game-of-life.c

#include <stdlib.h>
#include <stdio.h>

size_t width, height;
char *grid1, *grid2, *oldg, *newg;
unsigned seed;

void shuffle()
{
	size_t i, n;
	n = width * height;
	for(i=0; i<n; ++i)
	{
		oldg[i] = seed & 1;
		seed = (seed>>2) + (seed*771);
	}
}

void update()
{
	size_t i, j, k;
	for(i=0; i<height; ++i)
		for(j=0; j<width; ++j)
		{
			int const dx[] = {-1, 0, 1, -1, 1, -1, 0, 1};
			int const dy[] = {-1, -1, -1, 0, 0, 1, 1, 1};
			int n = 0;
			for(k=0; k<8; ++k)
			{
				size_t x = (j + dx[k]) % width;
				size_t y = (i + dy[k]) % height;
				if(oldg[x + y*width])
					++n;
			}
			if(oldg[j + i*width])
			{
				newg[j + i*width] = n == 2 || n == 3;
			}else{
				newg[j + i*width] = n == 3;
			}
		}
}

void show()
{
	/* reset the cursor */
	#ifdef _WIN32
		system("clear");
	#else
		fputs("\033[1;1H", stdout);
	#endif
	size_t i, j;
	for(i=0; i<height; ++i)
	{
		for(j=0; j<width; ++j)
		{
			char c = newg[j + i*width] ? '#' : ' ';
			putchar(c);
			putchar(c);
		}
		putchar('\n');
	}
}

int main()
{
	width = 40;
	height = 40;
	grid1 = (char *)malloc(width * height);
	if(!grid1)
		return 1;
	grid2 = (char *)malloc(width * height);
	if(!grid2)
		return 1;
	oldg = grid1;
	newg = grid2;
	seed = 123456;
	shuffle();
	puts(
"write q to quit\n"
"write r to restard the board\n"
"anything else to run\n"
	);
	for(;;)
		switch(getchar())
		{
		case 'q':
			free(grid1);
			free(grid2);
			return 0;
		case 'r':
			shuffle();
			break;
		default:
			update();
			show();
			oldg = newg;
			newg = newg==grid1 ? grid2 : grid1;
		}
}